Yttrium containing ferrous products and methods for preparing same



United States Patent Ofifice 3,055,756 Patented Sept. 25, 1962 This invention relates to unique ferrous alloys possessing improved properties, and processes for preparing the same, and, more particularly, to cast iron containing 1 small, but effective, amounts of yttrium.

It is known that the physical characteristics of ferrous metal containing carbon can be improved 'by forming the graphite in compacted, spheroidal, or nodular shapes. With the graphite in a compacted, or spheroidal, form, the metallic matrix is free of discontinuities, and possesses superior physical properties, particularly improved ductility. t

Gray iron has been made more ductile by addition to the molten iron containing graphite-yielding carbon, certain agents, such as cerium, magnesium, calcium, misch metal, and the other materials, in the elemental form, as alloys, as mixtures with inert substances, or as chemical compounds of the desired addition metal.

There are certain disadvantages to each of the above identified addition agents, a few of which can briefly be mentioned as illustrative of the problems involved. introducing elemental magnesium into molten ferrous metal is hazardous, since its boiling point, 1120 C., is below the melting point of a eutectic iron carbon solution, ordinarily maintained around 1500 C. The same disadvantage accompanies the introduction of elemental cerium, or calcium, since their respective boiling points are l400 C. and 1170 C.

Introducing the foregoing addition agents into a ferrous melt as alloys with metals, or non-metals, or as mixtures with inert materials, has the disadvantage of not only adding sometimes unwanted ingredients to the iron, but also of requiring materials which in some instances are costly or are not readily obtainable.

In the preparation of malleable iron, white iron has been treated with certain inoculating agents in order to sensitize the casting for carbon precipitation during the heat treatment.

It is, therefore, an object of the present invention to provide an improved process for effecting the formation of spheroidal, compacted, or nodular, granules of graphite in cast ferrous metal containing carbon. t is still another object of the invention to improve the physical properties of cast iron. It is still another object of the invention to provide an addition agent that is efhcient and effective, compared on a weight basis with previous addition agents, for the production of spheroidal carbon in iron. It is yet another object of the invention to provide a process for making spheroidal carbon iron using an addition agent which possesses a high vaporization temperature which improves the introduction into the ferrous metal. It is still another object of the invention to provide an addition agent for the manufacture of spheroidal carbon in iron which allows a high carbon Briefly stated, the invention is concerned with an iron casting containing from about 0.05% to about 0.8% by weight of yttrium, the balance a cast iron composition. The present invention also contemplates a process for manufacturing the above characterized ferrous metal containing carbon, by addition to the molten metal, a small, but eifective, amount of yttrium.

The composition of the novel ferrous product of the invention, in the absence of yttrium, is that of cast iron, for example gray iron, or white iron. Generally, the product will contain at least 50% by weight iron and usually at least 90% by weight iron, carbon and silicon in the cast iron range, for example, 2% to 5% by weight of carbon and 1% to 5% by weight of silicon. The yttrium retained in the product of the invention is in the range from about 0.05% to about 0.8%, usually from about 0.2% to about 0.8% by weight.

The micro-structure in one form of product of the invention is obtained in the as-cast condition with spheroidal, compacted, or nodular graphite and substantially devoid of the flake form. The nodular, or spheroidal, form of carbon is obtained in any matrix which as-cast, without a nodulizing agent, possesses flake graphite, such as gray cast iron. The various matrix constituents and structure can be controlled by well known methods by regulating the ingredients with or without heat treatments to obtain, for instance, pearlite, ferrite, martensite, tempered martensite, acicular transformation product of austenite, or combinations of the foregoing.

The addition of yttrium also enhances what would otherwise be white iron, in another form of the invention. If heat treatments of the white iron are employed, beneficial results are obtainable which are attributable to yttrium. Also, the presence of yttrium in white iron improves its physical characteristics, in some instances.

In carrying out the process contemplated by the invention, yttrium is introduced into the molten cast iron.

The yttrium may be added in its elemental form, as an alloy, or as a compound which, upon reaction, yields yttrium in elI'eotive amounts, by techniques previously known in this field. Because of the high melting and boiling points of yttrium, it can be added as an element with less danger than many other materials. However, some precaution need be taken so as to minimize the surface area of the addition agent, since the powdered form which has high exposed areas may cause the yttrium to react with explosive violence. For this reason, it may the desirable to introduce the yttrium in the form of a solid yttrium-containing agent, [for example, 20% by weight yttrium-% by weight silicon, or 20% by weight yttrium-45% by weight silicon-35% by weight iron alloys.

The amount of yttrium to be added to the bath will depend upon a number of conditions. If too large a quantity is retained in the product, iron carbide will Brinell Elonga- Reduction, tion of Hardness Percent Area,

Percent 4 TABLE IV Yield p.s.i.

ions are in accordance A-339-55, Standard Specifica- TABLE V Mechanical Properties Treatment N0. 1

Tensile Alloy N0. Strength, Strength result in the ascast structure. Too small amounts of yttrium Will fail to obtain the optimum nodulizing effect of the carbon. The constituents in the melt, the temperature of the molten iron, the contemplated delay in casting after introduction of yttrium, the proportion of re- 5 tained yttrium in the product, and the amount of retained yttrium desired will be factors to be considered. Addition amounts will, there-fore, be such as to obtain e foregoing tensile determinat with AS 1 requirements,

Mechanical Properties Treatment N0. 2

tion For Nodular Iron Castings.

lggrlcqent tained S 057464771171 5 566 94332232 19 111111111111 mem rrN m "vi M 000050000500 3 a mA d omd m md omfiwL nec 1 rr MAC R P m 500000050505 H uue E P m M m EH5 Ymo. t. S S .J n mu. Tt S m y o 1 A 194455230196298472 l 7 2131401222 200044W2-M1 00000000000000 00000000 The foregoing tensile determinations are in accordance with ASTM requirements, A-33955, Standard Specification For Nodular Iron Castings.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims or the equivalent of such be employed.

We, therefore, particularly point out and distinctly claim as our invention:

We claim:

1. The process for producing iron castings in which graphitic carbon is present in the nodular form and with substantially no separation of flake-like graphitic carbon which comprises the steps of preparing a bath of molten cast iron mix, introducing into said bath a small but effective amount of yttrium sufiicient to control occurrence of unconrbined carbon as substantially spheroidal particles,

and thereafter casting metal from said bath to produce a casting containing a small but effective amount of yttrium and containing graphite in a compacted form.

2. The process for producing iron castings in which Brinell F.-air cool.

Reduction of Hardness Area, Percent tion,

Treatment Elon ga- Percent TABLE I TABLE II .5 hours-furnace cool to 1000 F.air 45 .2 l1oursfurnace cool to 1325 F.-hold Yield TABLE III Chemical Analysis as east. 1325 F cool. 1750 F 20 hours furnace cool to 1000 p.s.i.

Tensile Strength, Strength,

lnmllllqaawnmawawamaawnaawnmaiid rm Mechanical Properties Treatment N0. 0

Alloy Treatment No.

Alloy N0.

The foregoing tensile determina with ASTM requirements, A-339-55, Standard Specifica- 0.8% by Weight of yttrium. tion For Nodular Iron Castings. 5. An iron casting comprising about 0.05% to about 0.8% by weight yttrium, and the balance a cast iron composition characterized by uncorn bined c-anbon particles dispersed in the ferrous matrix in the spheroidal form.

6. An iron casting comprising about 0.05% to about 0.8% by Weight yttrium, and the balance a gray cast iron composition characterized by unoom-bined carbon particles dispersed in the ferrous matrix in the spheroidal form.

7. An iron casting comprising about 0.05% to about 0.8% by Weight yttrium, and the balance a white cast iron composition characterized by uncombined carbon particles dispersed in the ferrous matrix in the spheroidal form.

8. An iron casting comprising at least 90% by Weight of iron, from about 0.05% to about 0.8% by weight yttrium, from about 1% to about 5% by Weight of silicon,

said casting being characterized by uncombined carbon being in the spheroidal form.

References Cited in the file of this patent UNITED STATES PATENTS 2,485,760 Millis et al. Oct. 25, 1949 2,488,511 Morrogh Nov. 15, 1949 2,488,513 Morrogh Nov. 15, 1949 2,750,284 Thrig June 12, 1956 FOREIGN PATENTS 721,717 Great Britain Jan. 12, 1955 OTHER REFERENCES Rate Metals Handbook, 1954, page 329. Edited by C. A. Hampel. Published by Reinhold Publishing Corp., New York. NY. 

5. AN IRON CASTING COMPRISING ABOUT 0.05% TO ABOUT 0.8% BY WEIGHT YITTRIUM, AND THE BALANCE A CAST IRON COMPOSITION CHARACTERIZED BY UNCOMBINED CARBON PARTICLES DISPERSED IN THE FERROUS MATRIX IN THE SPHEROIDAL FORM. 